Moments after Jennifer Mabley, half of the Water Mill–based interior design team Mabley Handler, walked into this newly built Amagansett six-bedroom for the first time, she had an epiphany. She cried out, perhaps a little too vehemently, "The best thing you can do for this house is get rid of the dropped ceiling in the kitchen. Show off the interior lines. Let the architecture speak!"

The house, built according to plans the homeowners had purchased, had a living room with an impressive 20-foot ceiling, but the adjacent dining room and kitchen were indeed cause for Mabley's astonishment, with low, flat ceilings that didn't do the rooms justice. Right above the kitchen, under the peaked roof at the center of the house's façade, was wasted space and a lost opportunity: an attic with an attractive oval window that could only be seen from outside.

Talk about a tight turnaround. Within a week of Mabley's impassioned outburst, the dropped ceiling in the kitchen was gone and the existing structural members had been clad with wood to give them a more finished appearance. The soaring, light-filled kitchen, with a new, decorative truss reminiscent of European barns and farmhouses, was finally worthy of its location at the heart of the house.

Before turning to the interior décor, Mabley and her husband, Austin Handler, completed further architectural upgrades, installing high-end panel doors, moldings and trims with a level of detail Handler calls "transitional. It's a Shingle-style house on the outside," he says, "so we didn't want to go totally modern." They also wrapped the double-sided fireplace that faces both the foyer and living room in raw poplar, tinted with a pale gray-white wash that leaves the wood grain visible, then ran the same poplar over the rib vaulting that traverses the living room's unusual gambrel ceiling.

The house is the primary residence of a couple with three grown children. When it came time to furnish, they made things very clear: they wanted the interiors to say "beach house," but not "casual beach house." "So 'sophisticated beach' became our mantra," Mabley recalls. "The rule was nothing gold, nothing yellow." Anything rustic was out, as were warm tones. The clients, pointed in their preferences, favored a cool palette—pale oyster gray with a hint of blue—that for them recalls the ocean and sandy beaches on a misty day. "The serene palette was a parameter that helped us zero in on a look and style," Mabley says.